Endothemic and Exothemic Reaction

ENDOTHERMIC AND EXOTHERMIC REACTIONS

By : Ni Luh Gede Enik Karnila Yanti

Chemistry Education Departement

Faculty of Mathematics and Natural Sciences

Ganesha University of Education

Abstract

Endothermic reaction is the reactions that release heat energy and exothermic reaction is the reactions that absorb heat energy. Heat energy is a form of energy that was received by an object, which causes the temperature of the object, is changed shape. The objective of this experiment was to differentiate endothermic and exothermic reactions. Endothermic reactions are show by decreasing of temperature. Exothermic reactions are show by increasing of temperature.

Key word: endothermic reactions, exothermic reactions

Introduction

Each change of substance would arise energy or absorption energy. Energy is the ability to do work (effort) (Chang Raymond, 2005).  Energy is released or absorbed may occur in the form of light energy, electricity energy and heat energy. Heat energy is a form of energy that is receives by an object, which causes the temperature of the object, is changed shape.  Heat and temperature are different. Heat is a quantity or amount of heat absorbed or released by an object. While the temperature as measure of the degree of heat in units owned by a substance. In general, to detect the presence of heat in a substance is to measure the temperature of the object. Energy is absorbed or released in the form of heat. It was measured with a thermometer. Reactions that release heat are calling exothermic reactions, whereas reactions that absorb heat are calling endothermic reactions (Chang Raymond 2010,). In the exothermic reaction, heat flows from the system into the environment so that the enthalpy of the system will be reduced, which means that the enthalpy of the product (Hp) is smaller than the enthalpy of the reactants (Hr). Therefore, enthalpy changes (ΔH) are negative.

Exothermic reaction: H = Hp-Hr < 0 (negative)

Endothermic reactions, heat absorb by the system from environment. Therefore, the enthalpy of the system will increase, meaning that the enthalpy of the product (Hp) is greater than the enthalpy of the reactants (Hr). As a result, changes enthalpy (ΔH) is positive.

                  Endothermic reaction: ΔH = Hp-Hr> 0 (positive)

This experiment aimed to differentiate endothermic and exothermic reactions.

            In studying the chemistry, not all can be learned through books, studied chemistry cannot only learn the theory. To improve understanding of students need to use the method of contextual learning. In the study material of exothermic and endothermic reaction is very important to include experiments in teaching learning process. With doing experiment students will more understand about the theory.

Materials and Methods

This experiment used some chemicals, such as calcium oxide solid (CaO), magnesium ribbon (Mg), hydrochloric acid solution (HCl) 1M, potassium nitrate solid (KNO₃), and water. The method used in conducting this experiment was adopted from an experiment procedure developed by Thoa Koei Ham and Sjahrial Gazali (1980:17-20)

Results and Discussions

The result of the experiments is presented in the Table below.

Table 1.Observation result of Calcium oxide (CaO) mix with water

Experiment	Observation Results
Measure the temperature of water	The temperature of water is 300C
Measure the temperature of water + calcium oxide	The temperature of water + calcium oxide is 320C

Table 2.Experiment result magnesium ribbon (Mg) in hydrochloric (HCl)

Experiment	Observation Results
Measure the temperature of hydrochloric acid (HCl)	The temperature of hydrochloric acid (HCl) is 310C
Measure the temperature of hydrochloric acid (HCl) + magnesium ribbon (Mg)	The temperature of hydrochloric acid (HCl) + magnesium ribbon (Mg) is 320C

Table 3.experiment result of dissolving potassium nitrate (KNO₃) in water

Experiment	Observation Results
Measure the temperature of water	The temperature of water is 300C
Measure the temperature of water + Potassium nitrate (KNO3)	The temperature of water + potassium nitrate (KNO3) is 250C

Discussion 

Experiment Part I (CaO is mix with water)

Initial temperature of water before adding CaO is 30⁰ C and the temperature increase becomes 32⁰C after adding CaO. Because the temperature increase means that reaction is exothermic reaction. Exothermic reaction can occur because heat flows from the system into the environment so that the enthalpy of the system will be reduced, which means that the enthalpy of the product (Hp) is smaller than the enthalpy of the reactants (Hr).

Experiment Part II(Mg ribbon mixed with HCl)

Initial temperature of HCl before adding Mg is 31⁰ C and the temperature increase becomes 32⁰ C after adding Mg. Because the temperature increase means that reaction is exothermic reaction. Exothermic reaction can occur because heat flows from the system into the environment so that the enthalpy of the system will be reduced, which means that the enthalpy of the product (Hp) is smaller than the enthalpy of the reactants (Hr).

Experiment Part III (dissolving of  KNO₃ in water)

      Initial temperature of water before adding KNO₃ is 30⁰ C and the temperature decrease becomes 25⁰ C. Because the temperature decreases means that reaction is endothermic reactions. Endothermic reactions can occur because heat absorb by the system from environment. Therefore, the enthalpy of the system will increase, meaning that the enthalpy of the product (Hp) is greater than the enthalpy of the reactants (Hr).

Conclusions

Based on discussion above, it can be conclude that CaO mixed with water form exothermic reaction. Mg ribbon mixed with HCl form exothermic reaction. Dissolving of  KNO₃ in water can form endothermic reaction.

References

Chang,Raymond.2005. Kimia Dasar Konsep-konsep Inti Jilid 1. Jakarta: Erlangga

Chang, R. 2010. Chemistry . (10th). New York: McGraw- Hill.